[EnergyPlus_Support] Re: Using AFN for windows, but with default infiltration

["allinson_louis" <allinson_louis@xxxxxxxxxxx>]

Thank you for this informative post. Plenty of food for thought. I was just wanting to ensure my model was 'equivalent' to other models I had seen (not using e+) which tend to model a standard 0.1ach as an assumption


which of course does not represent reality but apperas to be a typical assumption


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jeannieboef@..." <jeannieboef@...> wrote:
>
> Just saying a big "YES!" to Joe's comments.
> 
> Extra points are:
> 1) You could pretend there was a blower door test and ASSUME all leaks  
> in the closed possition are equally leaky per linear length. That  
> means measuring out all your modelled exterior facing leaks (example  

> top bottom sides of all modelled doors and windows). This allows you  
> to calculate the "per meter length leakage coefficient at 50 Pa for  
> example that is required for a desired air change for your facility by  
> using the normal power-law equation (Q = C*dP^n). Note that you'll  
> have to sum the total volume of the facility to convert the required  
> ACH to m3/s for the power-law equation. After you have calculated C  
> (assume C is the same at 1 Pa as at 50 Pa), you can place this same  
> input on each exterior leak object as discussed. This is currently my  
> prefered method for using AFN where a lot of assumptions must be made.
> 
> 2) Data-driven approaches aren't wrong as such. The downside is that  
> you rely heavily on the statistics you put to ground. For example, if  
> you have statistical infiltration data for 100 builings of similar  
> type and hvac to yours in your climate, then this is a viable option  
> for you, if you can live with the granularity of the data. In my  
> opinion this method should be used (normal infiltration objects) for  
> most mechanically ventilated buildings (opening events are usually far  
> less and at times where large temperature swings are unlikely). Where  
> I start getting irritated is using data-driven approaches to only- 
> window-ventilated buildings. The temperature swings and number of  
> venting occurances are huge and seriously affect user comfort, which  
> in turn effects the opening and closing of the windows --> heating of  
> outdoor air and energy consumption. The minute-wise data just isn't  
> there.
> 
> 3) A third approach is possibly the best. A data-driven approach with  
> stoastic modelling of the main factors which lead to when and for how  
> long a widow stays open (Anderson)...these factors would be inputs  
> into a formula which would open or close the window on a probability  
> threshold coupled to a randomness effect. Inputs which would increase  
> or decrease this probability are the usual:

> Temperature zone
> Temperature of outdoor air
> Time of year
> Solar
> Stuffiness of air possibly using CO2 as an indicator
> Number of people in the zone
> Number of people having entered the zone to stay in the zone from the  
> last timestep
> Room air velocity or windvelocity
> Etc.
> 
> 4) I've tried a bit of an advanced version of 1) (AFN + EMS control  
> algorithm for x2 widow groups, based on monitoring comfort criteria)  
> approach based mainly on PPD threshholds of comfort criteria including  
> CO2. The only thing I kept constant were that the persons in my  
> facility were evenly distributed (no human traffic modelling), but the  
> densities were indeed scheduled. It worked quite well to identify  
> problems with the design and possible solutions and demonstrated  
> typical expected CO2 concentrations for my design. It also showed the  
> problem that windows don't linearly modulate (even when split into two  
> independant groups per zone)...this means that occupants close windows  
> too quickly after the opening event in winter due to "cold draughts"  
> or intense temperature swings in the space. My model required 1 minute  
> timesteps to catch this effect. It also showed up the common problem  
> of controlling a heating system which is based on an air temperature  
> thermostat. I like this approach best, but would idealy prefer the PPM  
> threshholds still to be affected by an element of randomness and to  
> include the human traffic element (the most significant ones being the  
> venting upon the entry of a new person who is likely to stay AND the  
> venting of unoccupied rooms). My other significant assumption was  
> imposing a limit on the opening event frequency (not closing). I found  
> no data to base this assumption on.
> 
> Hopefully there was some food for thought in my rambles.
> 
> 
> Mit freundlichen Grü�en- Sent from my iPhone (excuse the brevity)
> 
> i. A.
> Jean Marais
> b.i.g. bechtold
> Tel.   +49 30 6706662-23
> 
> On 03.10.2013, at 19:21, Joe Huang <YJHuang@...>  
> wrote:
> 
> > I'm afraid you're missing the point.�� The original  
> > question was how to model infiltration when the AFN is being used.
> > My point was that you cannot mix the infiltration object in  
> > conjunction with the AFN.�� If you want to model  
> > infiltration with the AFN, you have to define the leakage characteri 
> > stics of the space for the AFN�� (this should probably be  
> > done anyway for proper modeling - in fact, all these AFN programs su 
> > ch as COMIS and AirNet were originally designed not for modeling nat 
> > ural ventilation, but rather infiltration).��
> >
> > Sure, you can use a blower door test to get the leakage fraction,  
> > but that has to be used as an input to the AFN, not to the  
> > infiltration object.���� I've always been adverse  
> > to modeling infiltration as a constant air change rate, because that 
> > 's nonphysical and not what really happens.�� IMHO, it's  
> > always much better to define the physical characteristics of the spa 
> > ce (leakage-fraction, area of cracks, etc.) and then use a physical  
> > model like the Sherman-Grimsrud or the AFN to then compute the hour- 
> > to-hour infiltration.
> >
> > Joe
> > Joe Huang
> > White Box Technologies, Inc.
> > 346 Rheem Blvd., Suite 108D
> > Moraga CA 94556
> > yjhuang@...
> > http://weather.whiteboxtechnologies.com for simulation-ready weather  
> > data
> > (o) (925)388-0265
> > (c) (510)928-2683
> > "building energy simulations at your fingertips"
> >
> > On 3/10/2013 9:25 AM, Oscar Hernandez wrote:
> >>
> >> There are many methods to calculate the real infiltration  
> >> value...like the blower test.
> >>
> >> On Oct 3, 2013 6:06 PM, <josep.sole@...> wrote:
> >> ��
> >> In AFN models you need to assume a lot of other hypothesis it is no  
> >> easier than assume the zone infiltration rate.
> >>
> >>
> >> ��
> >>
> >> Josep Sol��
> >> URSA Insulation S.A-
> >>
> >> Sustainibility & Technical Manager��
> >>
> >> M��vil +34 606 42 32 14
> >>
> >> www.ursa.es
> >>
> >> www.ursainsulation.com
> >>
> >> www.uralita.com
> >>
> >> ��<mime-attachment.gif>
> >> P URALITA / URSA se compromete con el ahorro de energ��a.  
> >> Antes de imprimir este mensaje aseg��rese de que es necesar 
> >> io.
> >>
> >> ��
> >>
> >> De: EnergyPlus_Support@xxxxxxxxxxxxxxx  
> >> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] En nombre de Oscar  
> >> Hernandez
> >> Enviado el: jueves, 03 de octubre de 2013 17:57
> >> Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >> Asunto: Re: [EnergyPlus_Support] Using AFN for windows, but with  
> >> default infiltration
> >>
> >> ��
> >>
> >> ��
> >>
> >> If you want to model an infiltration value use the zone  
> >> infiltration. The AFN its to predict the infiltrattion value when  
> >> you don"t know it.
> >>
> >> ��
> >>
> >> On 3 October 2013 17:42, Joe Huang  
> >> <YJHuang@...> wrote:
> >>
> >> ��
> >>
> >> I don't think the infiltration objects can be used in conjunction  
> >> with the AFN. That would violate the mass balance of the AFN,  
> >> wouldn't it?
> >>
> >> Sent from my IPad
> >>
> >> ��
> >>
> >> Joe Huang
> >>
> >> ��
> >>
> >>
> >> On Oct 3, 2013, at 8:35 AM, Oscar Hernandez <eng.ohw@...>  
> >> wrote:
> >>
> >> ��
> >>
> >> Hi,
> >>
> >> Use the zone infiltration.
> >>
> >> Oscar
> >>

> >> On Oct 3, 2013 2:48 PM, "allinson_louis"  
> >> <allinson_louis@...> wrote:
> >>
> >> ��
> >>
> >> Hi All
> >>

> >> I am using AFN to model air flow through window openings that I am  
> >> controlling using EMS
> >>
> >> However, when the windows are closed the only infiltration is  
> >> through cracks and the infiltration is much less than 0.1ach. I  
> >> want to model a 'default' 0.1ach when the windows are closed, as  
> >> this is a typical value used in simulations.
> >>
> >> Is this possible?
> >>
> >> ��
> >>
> >
>






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